This invention relates generally to mechanism for producing back and forth motion and more particularly to mechanism for converting rotary motion of a driving member into back and forth motion of a driven member. The invention has even more specific reference to a mechanism in which the driven member travels in a generally elliptical orbit as it moves back and forth.
Various types of mechanisms for converting rotary motion to back and forth motion are well known and are frequently incorporated in power operated tools. In such an instance, the driving member is usually the rotary drive shaft of a motor while the driven member is formed by a work-performing tool. The tool may be a saw blade, a file, a sanding device, a shaper or the like. The driven member may take forms other than tools such as, for example, a reciprocating pawl for driving a ratchet.
In some cases, the driven member or tool is simply reciprocated back and forth with a straight line motion. In other cases, the tool advantageously is moved in a substantially elliptical orbit so that the tool traces different paths during its advance and return strokes. In a jig saw, for example, the saw blade may be moved in a substantially elliptical orbit so as to cause the teeth of the blade to cut into the work during one half of the stroke and to pull free of the work during the return stroke. Because the blade pulls free of the work during the return stroke, the teeth do not rub reversely against the work and, in addition, sawdust and waste chips are more effectively removed from the cut. By forming teeth around the tip of the orbitally movable blade, the blade can be used for plunge cutting as well as for conventional cutting.
As mentioned above, back and forth movement of the tool is often effected in response to rotation of a shaft. One extremely simple manner of converting the rotary motion of the shaft into back and forth motion of the tool is to connect the tool to an eccentric on the shaft and to constrain the tool for movement along a desired path.